The present invention relates to combination brush and labyrinth seals for a rotary machine such as steam and gas turbines and particularly to split packing ring segments for receiving low-cost bendable brush seal inserts.
Rotary machines such as steam and gas turbines used for power generation and mechanical drive applications are generally large machines consisting of multiple turbine stages. High pressure fluid flows through the stages and must pass through a series of adjoining stationary and rotating components and seals therebetween. Seals between the stationary and rotating components are used to control leakage. Labyrinth-type seals are typically used in machines of this type and conventionally comprise labyrinth teeth spaced axially one from the other for controlling leakage between the rotating and stationary components. Examples of labyrinth seal usage includes interstage shaft seals, rotor end seals and blade tip seals.
More recently, brush seals have been employed in conjunction with packing ring segments and labyrinth seal teeth. Typically, a brush seal is installed in a groove or cell machined in a solid packing ring segment having one or more labyrinth teeth spaced axially from the tips of the bristles projecting from the concave surface of the packing ring segment. The brush seal normally consists of three components joined preferably by welding. These components include a forward plate, a backing plate and bristle pack disposed between the forward and backing plates. The brush seal, however, is a complex and costly component. It must be machined to precisely fit the diameter of the rotor against which it will bear as a seal. Because of the large number of rotor sizes, brush seals cannot be advance-ordered for retention in inventory but must be custom manufactured for each application, requiring extended cycle times. On the other hand, brush seals are very desirable. For example, brush seals have the ability to accommodate radial excursions of a rotor. They typically have the ability to closely control the gap between the forward plate and the bristle pack. The total width of the gap and the bristle pack is preferably on the order of 0.1 to 0.2 inches. A typical example of a combined labyrinth and brush seal for a rotary machine is described and illustrated in U.S. Pat. No. 6,105,967, of common assignee herewith. It is therefore desirable to provide a labyrinth/brush seal combination in a packing ring segment wherein a brush seal is adaptable to different diameters, producible at low cost and readily applied in the packing ring segment.
In accordance with a preferred embodiment of the present invention, there is provided a packing ring comprised of a plurality of packing ring segments each having a concave surface about an axis mounting one or more labyrinth seal teeth projecting from the surface. A chamber or cell is provided in the concave surface for reception of a brush seal insert. Each packing ring segment, however, is formed of two components secured one to the other by fasteners. The first component has a first surface which forms a backing plate for the bristles of the brush seal in the chamber. The second component has a second surface forming a forward surface in spaced opposition to the array of bristles forming the brush seal in the chamber. Thus, the brush seal forward and backing surfaces are integrally formed as part of the packing ring segment components. It will be appreciated that a generally T-shaped slot is formed in the packing ring segment to define the chamber, the base of the slot serving to retain the base of the brush seal insert in the slot. However, substantial width between the first and second surfaces has been needed in integral packing ring segments in order for a cutting tool to enter the bristle slot and machine the base of the T-slot into the packing ring segment, as well as the pressure balance grooves in the inner face of the backing plate. As a result, a fairly wide slot is necessarily formed. This has heretofore precluded the surface of the slot from forming the surface of the forward plate. That is, the wide slot prevents the forward surface from offering the same protection to the bristles as a narrow gap between the bristles and a forward plate would otherwise offer in conventional brush seals.
Also in accordance with a preferred embodiment hereof, the brush seal insert includes two very narrow strips along both sides of the weld at the top of the bristle pack. By using narrow strips, the brush seal can be readily bent over a significant range of diameters. Consequently, the brush seal insert can be provided in inventory in several standard diameter sizes and bent to the specific diameters needed within predetermined ranges. In order to accommodate the machining necessary to provide the base of the T-slot in each segment, as well as the pressure balance grooves, one aspect of the present invention provides for a packing ring segment formed of two components. A first component has a first surface which forms the backing plate for the bristles of the brush seal. The second component has a surface which forms the forward plate of the brush seal and is spaced in assembly from the bristle pack by a narrow gap. Thus, all of the machining required can be accomplished in each of the packing ring segment components prior to their assembly with the brush seal insert between the components in the brush seal chamber.
In one preferred embodiment of the present invention, the components are split along a plane normal to the rotary axis and passing through the chamber for the brush seal insert or one of the surfaces forming the forward or backing plate for the brush seal bristle pack. Thus, the bristle chamber can be formed to the required dimensions and the backing plate pressure balance grooves can be readily machined in the components. In a second embodiment, the packing ring segment is split from its concave sealing surface to the hook on its upstream side and along an arcuate surface radially inwardly of the hook toward the upstream side. Thus, the hook of the other component remains unbroken. The two components may be secured together by fasteners, such as threaded fasteners, bolts or the like.
In a preferred embodiment according to the present invention, there is provided a packing ring seal about a rotatable component comprising an arcuate packing ring segment for forming a portion of the packing ring seal and having a concave sealing surface, the segment including first and second discrete arcuate components in axial face-to-face relation to one another and secured to one another, the first and second components having first and second surfaces along respective faces thereof and axially spaced from one another defining a slot opening through the concave surface of the arcuate segment, an arcuate brush seal insert having an arcuate array of bristles disposed between the first and second surfaces and having bristle tips projecting from the segment along the concave surface thereof and at least one labyrinth seal tooth extending from the concave surface of the segment in spaced axial relation to the brush seal.
In a further preferred embodiment according to the present invention, there is provided for use in a machine having a component rotatable about an axis, a stationary component about the axis having an annular recess and at least one axially extending support carried by the stationary component about the axis and projecting into the recess, a packing ring comprising a plurality of packing ring segments for positioning about the axis, the segment having an arcuate seal face in opposition to the rotatable component and at least a first arcuate flange extending in an axial direction for cooperation with the one support to retain a portion of the packing ring segment in the recess, a generally T-shaped arcuate slot in the segment having an axially enlarged base and opening in a generally radial direction away from the base and toward the axis defining first and second axially opposed and spaced surfaces of the slot, a brush seal insert having a base element and a plurality of bristles extending from the base securing the bristles in the insert, the brush seal insert being disposed in the T-shaped slot with the base element received in the enlarged base of the slot and the bristles extending between the first and second axially spaced surfaces with the bristles abutting the first surface of the slot and spaced from the second surface thereof, the packing ring segment being split into a first component including the first surface and a second component including the second surface and means for securing the first and second components together with the brush seal bristles between the surfaces.